1. Field of the Invention
The present invention relates generally to a mobile communication system. In particular, the present invention relates to an apparatus and method for transmitting control information in a mobile communication system.
2. Description of the Related Art
Code Division Multiple Access (CDMA) mobile communication systems developed from a voice based IS-95 standard into a high-speed data transmission based IMT-2000 that also supports voice signal transmission. The IMT-2000 standard provides high-quality voice service, moving image service, and Internet search service.
In the mobile communication system, various schemes for servicing such information as voice and data are being realized, and a typical one of the schemes is a High Speed Downlink Packet Access (HSDPA) scheme in a Universal Mobile Telecommunications System (UMTS) communication system.
Generally, the HSDPA scheme refers to a data transmission scheme, including a high speed-downlink shared channel (HS-DSCH), which is a downlink data channel for supporting high-speed downlink packet data transmission, and its associated control channels. In order to support the high-speed downlink packet data service, an Adaptive Modulation and Coding (AMC) scheme, a Hybrid Automatic Retransmission Request (HARQ) scheme, and a Fast Cell Select (FCS) scheme have been proposed. A description will now be made of the HARQ scheme, especially, an n-channel Stop And Wait HARQ (n-channel SAW HARQ) scheme.
In the HARQ scheme, the following two methods have recently been applied to increase the transmission efficiency of an Automatic Retransmission Request (ARQ) scheme. According to a first method, retransmission request and Acknowledgement/Negative-Acknowledgement (ACK/NACK) are exchanged between a user equipment (UE) and a Node B. According to a second method, a UE temporarily stores defective data and combines the stored defective data with retransmitted data of the corresponding defective data before decoding the data. The high-speed downlink packet data service method has introduced the n-channel SAW HARQ scheme in order to compensate for the defect of the conventional Stop And Wait ARQ (SAW ARQ) scheme. In the case of the SAW ARQ scheme, next packet data cannot be transmitted before an ACK for a previous packet data is received. Therefore, in some cases, a UE should wait for an ACK even though it can currently transmit packet data.
In the n-channel SAW HARQ scheme, a UE continuously transmits a plurality of data packets before it receives the ACK for a previous data packet, thereby increasing channel efficiency. That is, if each of n logical channels established between a UE and a Node B can be identified by a specific time or its unique channel number, the UE receiving packet data at a specific time can determine a channel over which the packet data was received. Therefore, the UE can take necessary measures such as reordering data packets in their right reception order and soft-combining the corresponding data packets.
Table 1 and Table 2 below illustrate downlink and uplink physical channels used in a mobile communication system, respectively.
TABLE 1Downlink PhysicalChannelsFunctionsDPDCHDedicated Physical Data ChannelDPCCHDedicated Physical Control ChannelCPICHCommon Pilot ChannelP-CCPCHPrimary Common Control Physical ChannelS-CCPCHSecondary Common Control Physical ChannelSCHSynchronization ChannelPDSCHPhysical Downlink Shared ChannelAICHAcquisition Indicator ChannelAP-AICHAccess Preamble Acquisition Indicator ChannelPICHPaging Indicator ChannelCSICHCPCH (Common Packet Channel) Status IndicatorChannelCD/CA-ICHCPCH Collision Detection/Channel AssignmentIndicator ChannelHS-PDSCHHigh Speed-Physical Downlink Shared ControlChannelHS-SCCHHigh Speed-Shared Control Channel
TABLE 2Uplink PhysicalChannelsFunctionsDPDCHDedicated Physical Data ChannelDPCCHDedicated Physical Control ChannelPRACHPhysical Random Access ChannelPCPCHPhysical Common Packet ChannelHS-DPCCHHigh Speed-Dedicated Physical Control Channel
The downlink physical channels are distinguished using orthogonal variable spreading factor (OVSF) codes.
In order to support a packet data service with an uplink in a mobile communication system, a similar scheme to the scheme for supporting a packet data service with a downlink can be introduced. Therefore, in order to provide a packet data service in an uplink, it is necessary to transmit packet data of the uplink and control information of the downlink. The control information refers to, for example, “ACK/NACK information.” A scheme for transmitting control information including the ACK/NACK information using the downlink is classified into a scheme for transmitting the control information over an existing physical channel after time multiplexing, and a scheme for transmitting the control information over the existing physical channel after code multiplexing.
The time multiplexing scheme and the code multiplexing scheme will be described herein below with reference to FIGS. 1 and 2, respectively.
FIG. 1 illustrates a structure of a downlink physical channel for time-multiplexing ACK/NACK information, control information, with data before transmission. The types and functions of physical channels in the downlink have been illustrated in Table 1. Referring to FIG. 1, the ACK/NACK information which is control information is time-multiplexed to a space generated by puncturing data on a physical channel, before being transmitted. That is, the physical channel includes the ACK/NACK in a partial duration where no data is transmitted, before being transmitted.
FIG. 2 illustrates a structure of a downlink physical channel for code-multiplexing ACK/NACK information, control information, with an existing physical channel before transmission. Referring to FIG. 2, a separate physical channel for transmitting ACK/NACK information is generated in addition to an existing physical channel, and the ACK/NACK information is transmitted over the generated physical channel. The existing physical channel and the physical channel for transmitting the ACK/NACK information are separated using OVSF codes, as described above. Also, the physical channel for transmitting the ACK/NACK information can include control information indicating an ACK/NACK information transmission channel.
The time multiplexing scheme illustrated in FIG. 1 should include the ACK/NACK information which is control information in a partial duration of an existing physical channel, causing a possible loss of data transmitted over the existing physical channel. Although the code multiplexing scheme illustrated in FIG. 2 prevents data loss in the existing physical channel, it requires additional power and OVSF codes for the physical channel generated to transmit the ACK/NACK information which is control information.